My friend has a 99 Chevy 2500 extcab 4x4. He has a switch on his dash that reads "4x4 auto" and then some other choices.

We drove around in it today in a pretty heavy snow storm and it performed pretty well in that mode. (tires are AT, not even officially SNOW tires)

Is that the same as auto lock on Super Duties for the front hubs? He sais it locks the front hubs automatically in that mode but i'm not so sure....

Thanks

 

Wow, what is this? The fourth time in the past two weeks that this same question has been asked?

The Super Duty's have the manual locking hubs and the switch on the dash that allows you to shift into 4wd hi on the fly or 4wd lo while stopped and in neutral. The manual hubs are usually only used if the vacuum lines on the automatic system fail. I have never locked mine using the manual locks on the wheels. You can read more here:

Locking hubs.. What years and models?

and here:

locking hubs on 2005 250

and here:

4WD Locking hub Rim question...

 

Thanks, but what i'm trying to figure out is if his 99 Chevy 2500's "auto 4x4" is locking the front hubs. I mean, he doesnt have the ability to select "auto" or "lock" while also having another switch or shifter to activate 4hi or 4low, etc.........
On SuperDuties as I understand it, they have the hub switch in addition to the 4hi and 4low switch, correct? Please forgive my ignorance to this matter........

 

The auto 4x4 system on chevy's will engage 4hi when rear wheel slip is detected. It will return to 2hi if continued slippage is not detected. So, the truck is in 4hi until slip is not detected. Also, the chevy's hubs don't lock and unlock in the true sense of the definition, they spin all the time and the transfer case does all the switching back and forth.

 

Hmmm.. almost like an AWD system?

 

Similar, but most AWD systems have a differential in the transfer case, and use clutch packs or other devices to send power where needed. That's why true 4x4 systems bind up on pavement, because of the hard link between the front and rear axles. The reason for the binding is that in a part-time 4WD set up, there is no differential in the transfer case, as there is in an AWD setup (also called full-time.) The front axle travels a different arc than the rear axle, and with no differential, they are both mechanically connected to travel at the same speed, and you'll get binding as you said. Full time 4x4 systems like on a Land Cruiser or something similar have a diff in the center that is locked with a dash button to truely engage 4hi.

This system actually engages 4hi (if only for a moment) when slip is detected. If prolonged slip is detected, it will switch over to 4hi and stay there.

 

That's what I figured - my wife's Saturn Vue is the type of AWD set up with the clutch pack set up. Obviously NOT true 4X4...

Thanks!

 

Another example of this is the Ford Escape.

 

Sorry, I misunderstood. That system is really nice as it engages 4wd when the rear wheels start to slip. It's like the best of both worlds.

You can leave it in 4 wheel auto and it acts like an AWD, except that a true AWD system will vary torque to the front wheels(or rear wheels on FWD vehicles) up to 50% as needed. In 4 wheel auto, when rear wheel slippage is sensed, it simply locks the front hubs (or rear hubs on FWD vehicles) and directs 50% of the torque to the front.

When you switch into 4 wheel hi, it locks the front hubs and 50% of the torque is directed to the front wheels at all times.

My daughter's 2003 Explorer has the 4 wheel auto and it works great. The only downside is that when the front differential is locked, it can be hard to turn at times.

 

Great info... Thanks a bunch...